well lol i have the same problem with my "sack" you can use baby powder on where it sticks, with your 7inch penis, im not sure, you cant really hide an erection lol im 13 also but i am a late bloomer so mine is 2in nonerect and abou 3-4 erect, lol hope this helped

Mine is the same way, but well, im cut, my penis kind of gos up, and not so stright, so i tuck the head of my penis under the waist of my pants or boxers.